Multiport power converter with load detection capabilities

ABSTRACT

Power converters are provided that convert alternating current (AC) power to direct current (DC) power. A power converter may have multiple ports. Each port may have an associated connector with multiple power and data terminals. When an electronic device is connected to a given port, the electronic device draws DC power from the power converter. To ensure that the capacity of the power converter is not exceeded when multiple devices are connected to the ports of the power converter, the power converter may actively monitor its ports for active loads. Load detection circuitry can determine what number of ports are active. Control circuitry can compute a per-port available DC power level based on the number of active ports and can provide this information to connected devices.

BACKGROUND

This relates to power converters, and more particularly, to multiportpower converters.

Power converter circuitry can be used to convert alternating current(AC) power into direct current (DC) power. AC power is typicallysupplied from wall outlets and is sometimes referred to as line power.Electronic devices include circuitry that runs from DC power. The DCpower that is created by an AC-to-DC power converter may be used topower an electronic device. The DC power that is created may also beused to charge a battery in an electronic device.

In some applications, AC to DC power converter circuitry may beincorporated into an electronic device. For example, desktop computersoften include AC to DC power converter circuitry in the form of computerpower supply units. A computer power supply unit has a socket thatreceives an AC power cord. With this type of arrangement, the AC powercord may be plugged directly into the rear of the computer to supply ACpower without using an external power converter.

Although desktop computers are large enough to accommodate internalpower supplies, other devices such as handheld electronic devices andportable computers are not. As a result, typical handheld electronicdevices and laptop computers require the use of external powerconverters. When untethered from the power converter, a handheldelectronic device or portable computer may be powered by an internalbattery. When AC line power is available, the power converter is used toconvert AC power into DC power for the electronic device.

Compact AC-DC power converter designs are typically based onswitched-mode power supply architectures. Switched-mode power converterscontain switches such as transistor-based switches that work inconjunction with energy storage components such as inductive andcapacitive elements to regulate the production of DC power from an ACsource. A feedback path may be used to tap into the converter output andthereby ensure that a desired DC voltage level is produced under varyingloads.

Some power converters have more than one port. This allows multipledevices to be powered at a single time, but requires that the powerconverter be capable of delivering sufficient power to satisfy aworst-case scenario when all ports are occupied. The need toover-provision a power converter in this way to accommodate worst-casescenarios can lead to undesirable increases in the size and cost of thepower converter.

SUMMARY

An alternating-current (AC) to direct-current (DC) power converter mayhave multiple ports. The ports may have connectors such as universalserial bus connectors that allow cellular telephones, media players, orother devices to be connected to the power converter. When a port isoccupied by an electronic device, DC power may be conveyed to thatelectronic device to power the electronic device. For example, a batteryin the electronic device may be recharged.

In some situations, only a single port will be occupied. In othersituations, a user may plug electronic devices into two or more ports.Because the resources of the power converter are limited, there may be adesire to limit the amount of DC power that is delivered to each portwhen all of the ports are occupied.

The power converter may contain load detection circuitry. For example,voltage detector circuitry in a control circuit may monitor the voltagedrop that develops across current sensing resistors that are connectedin series with the ports of the power converter. When a current issensed using one of the current sensing resistors, the control circuitrycan conclude that an active load is connected to the power converter.

More sensitive load current measurements may be made using a controlswitch and a current-limited voltage regulator. A current-limitedvoltage regulator may be coupled to a positive power supply outputterminal in a port. The switch may be connected in series with theoutput terminal and may be periodically opened using the controlcircuitry. The voltage regulator may be based on a booster circuit thatproduces an output voltage that is larger than the nominal power supplyvoltage on the output terminal. When the switch is opened, controlcircuitry in the power converter can monitor the voltage on the outputterminal. If no load is present, the output voltage will rise to thevalue produced at the output of the current-limited voltage regulatorbooster circuit. If an electronic device is connected to powerconverter, the current drawn by the electronic device will exceed thecapacity of the voltage regulator, causing the output voltage to sag.

The power converter can use the current sensing resistors and other loaddetection circuitry to monitor the ports in the power converter andthereby determine what number of ports are connected to electronicdevices or other active loads. The power converter can then compute theamount of available power per port (i.e., the per-port available DCpower) based on the number of active ports.

The amount of power that is delivered to each electronic device can beregulated using control switches. Each electronic device that isconnected to the power converter can also be informed of the per-portavailable power level. This information can be conveyed to theelectronic devices using voltage codes (as an example). A pair ofvoltages may, for example, be produced on a pair of data lines in eachport. More complex digital communications schemes may also be used toconvey per-port available power information (e.g., serial and parallelbuses, bidirectional and unidirectional paths, links that usesynchronous or asynchronous communications, etc).

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and the followingdetailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of a system including a multiport power converterto which a single electronic device has been attached in accordance withan embodiment of the present invention.

FIG. 1B is a diagram of a system including a multiport power converterto which multiple electronic devices have been attached in accordancewith an embodiment of the present invention.

FIG. 2 is a circuit diagram of an illustrative multiport power converterin accordance with an embodiment of the present invention.

FIG. 3 is a circuit diagram of illustrative circuitry that may be usedin a multiport power converter to convey port power capacity informationto equipment that is connected to the power converter in accordance withan embodiment of the present invention.

FIG. 4 is a circuit diagram of a configurable voltage divider withmultiple control transistors that may be used in a multiport powerconverter to convey port power capacity information to equipment that isconnected to the power converter in accordance with an embodiment of thepresent invention.

FIG. 5 is a circuit diagram of illustrative control circuitry anddigital-to-analog converter circuitry that may be used in a multiportpower converter to convey port power capacity information to equipmentthat is connected to the power converter in accordance with anembodiment of the present invention.

FIG. 6 is a flow chart of illustrative steps involved in operatingmultiport power converter circuitry in accordance with an embodiment ofthe present invention.

DETAILED DESCRIPTION

Power converters can be used to convert alternating current (AC) powerinto direct current (DC) power. The DC power that is produced by a powerconverter can be used to power an electronic device. When powered inthis way, a rechargeable battery in the electronic device may berecharged.

Portable power converters are often used to power portable electronicdevices. These portable electronic devices may include laptop computers,handheld electronic device, cellular telephone, media player,accessories, etc.

To reduce size and save weight, AC-DC power converters may be formedusing switched-mode power supply architectures. In AC-DC powerconverters having switched-mode power supply designs, transistor-basedswitches are used in conjunction with energy storage components such asinductors and capacitors to regulate the production of DC power from anAC source.

Size and weight can be minimized by ensuring the transistor-basedswitches, energy storage components, and other circuitry of a givenpower converter are not overly large. In general, these componentsshould be sized according to the expected power delivery requirementsfor the power converter.

Conventional power converters are often provided with hardwired cablesand connectors. For example, a conventional power converter may have anAC connector that fits into a wall outlet and may have a DC connectorthat fits into a particular type of electronic device. The AC connectormay be provided at the end of an AC power cord. The DC connector may beprovided at the end of a DC power cable that couples the DC connector tothe main body of the power converter. A user who desires to power theelectronic device from a conventional power converter of this type canplug the AC connector into a wall outlet and can plug the DC connectorinto a mating connector on the electronic device. Conventional powerconverters such as these are only compatible with a particular type ofelectronic device and can only be used to power a single electronicdevice at one time.

To address these shortcomings, it may be desirable to provide moreflexible power converters. For example, a power converter can beprovided with multiple ports to which DC power cables can be connected.A power converter may, for example, have multiple Universal Serial Bus(USB) ports. Each USB port may have an associated connector that isadapted to receive a mating USB connector on a USB cable. If the userdesires to power a single electronic device, that electronic device canbe coupled to the power converter by plugging one end of a cable intothe electronic device and by plugging the other end of the cable intoone of the USB ports on the power converter. Because the power converterhas multiple ports, it is also possible to power multiple electronicdevices at the same time. If, for example, a user desires to power twodevices simultaneously, a first device may be powered using a first ofthe USB ports on the power converter and a second device may be poweredusing a second of the USB ports on the power converter.

To ensure proper operation of the power converter, the power convertermust have the capacity to satisfy the power demands of the electronicdevices that are connected to the power converter. To avoidover-provisioning the power converter and to thereby allow the size andweight of the power converter to be minimized, it may be desirable toprovide the power converter with intelligent load detection and powerdelivery capabilities. Particularly when the power converter hasmultiple ports, the power converter may sometimes be needed to supplydifferent amounts of power to different ports. Load detection and powerdelivery adjustment capabilities allow the power converter and attachedelectronic devices to be reconfigured to meet changing needs.

Consider, as an example, power converter 12 of FIGS. 1A and 1B. In thesituation illustrated in FIG. 1A, there is only one electronic device 10that is connected to power converter 12 (i.e., device A). In thesituation illustrated in FIG. 1B, there are two electronic devices 10that have been connected to FIG. 1B (i.e., device A and device B).Devices 10 may be cellular telephones, media players, portablecomputers, handheld computing equipment, or other electronic devices.Power converter 12 can sense which ports are active and can use eachport to deliver an appropriate amount of power so that the capacity ofpower converter 12 is not exceeded.

For example, in the situation of FIG. 1A, power converter 12 can deliver10 W of power to device A, whereas in the situation of FIG. 1B, powerconverter 12 can deliver 5 W of power to device A and 5 W of power todevice B. In this example, power converter 12 has a maximum capacity of10 W. When only a single device is drawing power, this capacity can bededicated to powering that single device (e.g., device A of FIG. 1A).When two devices are drawing power as shown in FIG. 1B, the 10 W totalcapacity of converter 12 can be shared between device A and device B. Toensure that devices A and B do not draw more than 5 W each, devices Aand B may be informed by converter 12 that there is only a maximum poweravailable of 5 W per port. Power regulation circuitry can also be usedin converter 12 to ensure that per-port power limits are not exceeded.

Converter 12 can inform attached devices of the available per-port powerlimit using voltage codes, resistive codes, serial or parallel digitalcommunications, using asynchronous communications, using synchronouscommunications, etc. Prior to communicating the maximum per-portavailable power to attached devices, converter 12 can examine each portto determine whether a load is attached. From this load monitoringoperation, converter 12 can calculate how many devices are connected toconverter 12. By determining what number of devices are connected toconverter 12 using load detection circuitry, converter 12 and can usethis information to determine the maximum per-port available power(i.e., by dividing the maximum capacity of converter 12 by the number ofconnected devices).

As shown in FIGS. 1A and 1B, AC power can be provided to converter 12from AC source 14 (e.g., an AC wall outlet). The AC line power fromoutlet 14 may be converted into DC power by converter 12 (e.g., using aswitched-mode power supply design). Although AC-DC converters aresometimes described herein as an example, converter 12 may, in general,be any suitable type of converter (e.g., a DC-DC converter, etc.).Converter 12 may have multiple ports (e.g., port A, port B, etc.). Theremay be, for example, two ports in converter 12, three ports, four ports,more than four ports, etc. Arrangements in which converter 12 has twoports are sometimes described herein as an example.

As shown in FIGS. 1A and 1B, there may be connectors associated with theports of converter 12. For example, connectors 20A may be associatedwith a first port, connector 20B may be associated with a second port,etc.

Electronic devices 10 may also have connectors (e.g., 28A, 28B, etc.).Cables such as cables 18A and 18B may be used to interconnect converter12 and devices 10. For example, cable 18A may have a first connector 22Athat plugs into mating connector 20A of converter 12 and may have asecond connector 24A that plugs into mating connector 28A of device 10.Cable portion 26A may contain conductive lines (e.g., wires) thatconnect the terminals of connector 22A to the terminals of connector24A. Device B and other devices may likewise be coupled to converter 12.For example, device B may have a connector 28B that is coupled toconnector 20B of a second port in converter 12 using connector 24B,cable portion 26B, and connector 22B of cable 18B, as shown in FIG. 1B.The use of cables such as cables 18A and 18B to connect one or moredevices 10 to respective ports of converter 12 is merely illustrative.If desired, converter 12 may have ports that receive electronic devices10 directly (with no intervening cables) or that are connected todevices 10 using hardwired cables (e.g., cables that are integrated withconverter 12 and that do not include connectors such as connectors 22Aand 22B).

The connectors of converter 12 such as connectors 20A and 20B may be USBconnectors (e.g., female USB connectors for receiving mating male USBplugs on cables 18A and 18B). The connectors on devices 10 may be USBconnectors, 30-pin connectors, or other suitable connectors.

Illustrative circuitry for power converter 12 is shown in FIG. 2. Powerconverter 12 of FIG. 2 is a two port power converter that converts ACpower from AC source 14 to DC power on ports A and B. This is, however,merely illustrative. In general, power converters, which are sometimesreferred to as power adapters, can be used to convert any suitable typesof power. For example, a power converter may be used to boost or reducea DC power level. Power converters such as power converter 12 of FIG. 2that can be used in converting AC power to DC power are sometimesdescribed herein as an example. In general, however, the power convertercircuitry may include circuitry for transforming any suitable inputsignal (e.g., AC or DC currents and voltages) into any suitable outputsignal (e.g., boosted, reduced, or otherwise transformed AC or DCcurrents and voltages). The use of power converters such as AC-to-DCpower converters that produce regulated DC output voltages from AC inputsignals is merely illustrative.

As shown in FIG. 2, power converter 12 may be plugged into a source ofAC line power (source 14) such as a wall outlet. The AC power source mayprovide power at 120 volts or 240 volts (as examples). Circuitry in thepower converter such as AC-DC power converter circuit 122 may convertthe AC line power that is received into DC power. For example, an AC toDC power converter may receive AC line power at an input and may supplyDC power at a corresponding output. The output voltage level may be 12volts, 5 volts, or any other suitable DC output level.

The circuitry of AC-DC power converter circuit 122 may be based on aswitched mode power supply architecture. Switched mode power suppliesuse switches such as metal-oxide-semiconductor power transistors andassociated control schemes such as pulse-width modulation controlschemes or frequency modulation control schemes to implement powerconversion functions in relatively compact circuits. When the switchingcircuitry has a first configuration, power is transferred from a powersource to a storage element such as an inductor (e.g., a transformer) ora capacitor. When the switching circuitry has a second configuration,power is released from the storage element into a load. Feedback may beused to regulate the power transfer operation and thereby ensure thatthe output voltage is maintained at a desired level. Examples ofswitched mode power supply topologies that may be used in a powerconverter include buck converters, boost converters, flyback converters,etc.

With one suitable arrangement, which is sometimes described herein as anexample, AC to DC power converter circuit 122 may be implemented using avoltage rectifier and flyback converter. The voltage rectifier convertsAC line power from AC source 14 into DC power at a relatively highvoltage level. The flyback converter portion of the power convertersteps down the DC power at the output of the rectifier circuit to 12volts, 5 volts, or other suitably low level for operating circuitry inan electronic device. This low level DC output voltage may be presentedacross outputs 64 and 70. If desired, other power converterarchitectures may be used. The use of a switched mode power converterarrangement that is based on a flyback converter design is merelyillustrative.

Load detection circuitry may be provided in power converter 12 to allowpower converter 12 to detect which ports are occupied by attached loads(i.e., which ports are coupled to electronic devices 10 of FIGS. 1A and1B). In general, an AC to DC power converter or other circuit thatincludes load detection circuitry may supply DC power to any suitableload. Arrangements in which electronic devices 10 serve as loads forpower converter 12 are sometimes described herein as examples.Electronic devices that may receive DC power from power converter 12include a handheld computer, a miniature or wearable device, a portablecomputer, a desktop computer, a router, an access point, a backupstorage device with wireless communications capabilities, a mobiletelephone, a music player, a remote control, a global positioning systemdevice, a device that combines the functions of one or more of thesedevices, etc.

Electronic devices 10 (not shown in FIG. 2) may be connected to theterminals of ports A and B. Only two ports are shown in FIG. 2, butpower converter 12 may have additional ports if desired. Each electronicdevice 10 may have a battery for use in powering the device whenunattached to power converter 12. When power converter 12 is pluggedinto AC power source 14 and when a given electronic device is connectedto power converter 12, power converter 12 can transform AC power that isreceived from AC power source 14 into DC power for that device.

Each port in converter 12 may have a connector. The connectors may haveany suitable number of terminals. For example, devices 10 may each havea 30-pin connector universal serial bus (USB) port into which a USBcable may be plugged. The USB cable may be used to convey DC powerbetween a respective one of connectors 20A and 20B in power converter 12and electronic device 10. In the example of FIG. 2, each port and itsassociated connector in converter 12 has four USB-type terminals. Thesefour terminals include two power terminals P (positive power) and G(ground). These four terminals also include two data lines DP and DN.When a mating USB plug is connected, power can be delivered to aconnected electronic device over the P and G power lines. Data lines DPand DN may be used to convey information to the attached device (e.g.,information on a desired power draw setting for the attached device).

As shown in FIG. 2, the positive power terminal P in connector 20B maybe connected to positive power supply line 72A and the positive powerterminal P in connector 20A may be connected to positive power supplyline 72B. Lines 72A and 72B may be use to convey a positive DC voltageat 12 volts, 5 volts, or other suitable positive DC voltage level. ThisDC voltage level is sometimes referred to as Vbus (i.e., Vbusa for portA and Vbusb for port B) and corresponding lines 73A and 73B aresometimes referred to as power supply buses or output lines. The groundterminal G in connector 20B may be connected to ground power supply line74B and the ground terminal G in connector 20A may be connected toground power supply line 74A. Ground lines 74A and 74B may be coupled toground nodes 75A and 75B and to ground output 70 of AC-DC powerconverter circuit 12 and may be used to convey a ground voltage at 0volts or other suitable ground voltage level.

When connected to power converter 12, each electronic device 10 mayreceive DC power through the power pins of the USB connector and cable(as an example). The use of a USB connector to connect power converter12 and electronic device 10 is, however, merely illustrative. Anysuitable plugs, jacks, ports, pins, or other connectors, may be used tointerconnect power converter 12 and electronic devices if desired.Similarly, a hardwired connection or a suitable plug, jack, port, pinstructure, or other connector may be used to connect power converter 12to power source 14.

AC-DC power converter circuit 122 may convert AC power from AC source 14to DC power on output paths 64 and 70. Path 64 may be a positive powersupply line that is coupled to converter output line 73A viaseries-connected current sensing resistor RA and switch SWA and that iscoupled to converter output line 73B via series-connected currentsensing resistor RB and switch SWB. The circuitry of converter 12 suchas resistors RA and RB can be used to detect when an electronic deviceis attached to a port. When an active device is attached to a givenport, current flows across the current sensing resistor that isassociated with that port. For example, when a device is connected toport A, current may flow across resistor RA. This can produce ameasurable voltage drop across the voltage probe lines that areconnected across the resistor.

As shown in FIG. 2, voltage measurements lines 80A and 82A may be usedto route voltage measurement signals from resistor RA to controlcircuitry 54, whereas voltage measurement lines 80B and 82B may be usedto route voltage measurement signals from resistor RB to controlcircuitry 54. Control circuitry 54 may include voltage detectorcircuitry that uses lines 80A, 80B, 82A, and 82B to measure the currentsflowing through each port.

The magnitude of the voltage across resistor RA is indicative of thecurrent flowing through port A. The magnitude of the voltage acrossresistor RB corresponds to the amount of current flowing through port B.Because the magnitude of the current sensing resistors RA and RB may bedetermined in advance, measurement of the voltages across resistors RAand RB can be used to determine the amount of current flowing througheach port from Ohm's law. This calculation may be made by controlcircuitry 54 or other circuitry in converter 12. Control circuitry 54may include one or more microprocessors, digital signal processors,microcontrollers, memory circuits, hardwired processing circuits,analog-to-digital and digital-to-analog converter circuits,communications circuits, etc.

Path 70 may be a ground power supply line that is coupled to groundoutputs 75A and 75B of converter 12. Switching circuitry such asswitches SWA and SWB may be based on any suitable electrical componentsthat can control the flow of DC power from the output of AC-DC powerconverter circuit 122 to the power supply input lines associated withattached loads (i.e., the inputs of an electronic device that areconnected to the output port power supply lines in converter 12). Forexample, switches SWA and SWB may be implemented using one or moretransistors such as one or more power field-effect transistors (powerFETs).

Consider an example in which an electronic device is connected to portA. During normal operation, power converter 12 may use AC-DC powerconverter circuit 122 to supply a DC power supply voltage on lines 64and 70. Control circuitry 54 will close switch SWA, so line 64 will beshorted to output line 73A in port A. This allows the DC power supplyvoltages at the output of AC-DC power converter circuit 122 to beprovided to the electronic device via outputs 72A and 74A. The circuitryof port B may operate in the same way.

AC-DC power converter circuit 122 may contain control circuitry 38 forcontrolling internal switching circuits (e.g., transistor-basedswitches). The control circuitry may be responsive to feedback signals.For example, if port A is active, a feedback path that is formed usingline 60A, control circuitry 54, and isolation stage 78 in path 76 may beused to supply AC-DC power converter circuit 122 with information on thecurrent level of voltage Vbusa on output line 73A. In response to thisfeedback information, the control circuitry in AC-DC power convertercircuit 122 (i.e., control circuitry 38) can make real-time adjustmentsto the amount of DC voltage that is being supplied to the output ofAC-DC power converter circuit. For example, if the DC voltage on output64 has a nominal value Vsec of 5 volts and feedback indicates that thevoltage has undesirably risen to 5.05 volts, the control circuitry inAC-DC power converter circuit 122 can make adjustments to lower the DCoutput voltage back to the nominal value (Vsec). If port B is activewhile port A is inactive, feedback of this type can be derived fromfeedback path 60B. When both ports A and B are active at the same time,control circuitry 54 may monitor either line 60A or 60B, may monitorboth lines to produce an average feedback signal, or may monitor output64 using a separate feedback path (as examples).

Power converter 12 may contain an energy storage circuit 50. Energystorage circuit 50 (sometimes also referred to as an energy storageelement) may be based on any suitable circuitry for storing energy. Asan example, energy storage circuit 50 may include one or more batteries,capacitors, etc. During operation of power converter 12 when AC-DC powerconverter circuit 122 is supplying power to output path 64, a path suchas path 66 may be used to route power to energy storage circuit 50. Thepower that is routed to energy storage circuit 50 in this way may beused to replenish the battery, capacitor or other energy storagecomponents in circuit 50. In the example of FIG. 1, energy storagecircuit 50 is coupled to AC-DC power converter circuit 122 by paths 64and 66 (and ground 70). This is, however, merely illustrative. Anysuitable routing paths may be used to supply replenishing power fromAC-DC power converter circuit 122 to energy storage circuit 50 ifdesired.

Control circuitry 54 may monitor the status of power converter 12 usingpaths such as paths 80A, 80B, 82A, 82B, 66, 60A, and 60B. Whenappropriate, monitor 54 may provide control signals to AC-DC powerconverter circuit 122 using paths such as path 76.

An isolation element such as isolation stage 78 may be interposed inpath 76. The control signals that are provided over path 76 may be usedto direct control circuitry 38 to make adjustments to the operation ofconverter circuit 122 (e.g., to increase or decrease the output voltageon line 64 and/or to place AC-DC power converter circuit in anappropriate operating mode). In general, any suitable number ofoperating modes may be supported by AC-DC power converter circuit 122.

For example, AC-DC power converter circuit 122 may be placed in one ormore active modes and an optional standby mode. When in an active mode,AC-DC power converter 122 is on and supplies DC output power forreplenishing energy storage circuit 50 and for supplying power to portsA and B. In standby mode, which is sometimes referred to as a sleep modeor low-power mode, AC-DC power converter circuit 122 is placed in astate in which little or no power is consumed by AC-DC power convertercircuit 122 (i.e., AC-DC power converter circuit 122 is turned off byinhibiting modulation of its switched-mode power supply switches). Ifdesired, AC-DC power converter circuit 122 may have multiple lower powerstates (e.g., a partly off state and a fully-off state).

When AC-DC power converter circuit 122 is in standby mode, AC-DC powerconverter circuit 122 is off and allows output 64 to float. In thissituation, the power that has been stored in energy storage circuit 50may be delivered to path 66 from within energy storage circuit 50. Forexample, if energy storage circuit 50 contains a battery or a capacitor,the battery or capacitor may be used to supply a battery or capacitorvoltage to path 66. The voltage supplied by energy storage circuit 50may be supplied at the same voltage level as the nominal output voltagelevel (Vsec) that AC-DC power converter circuit 122 supplies to path 64when AC-DC power converter circuit 122 is in active mode.

Voltage regulators 52A and 52B may be current-limited circuits thatproduce output voltages that differ from the nominal output of AC-DCpower converter circuit 122. Voltage regulators 52A and 52B may, forexample, be current-limited booster circuits that each produce an outputof 5.1 volts (as compared to the 5 volt output of AC-DC power convertercircuit 122). Periodically, control circuitry 54 can test whether a loadis present on a given port by opening the switch for that port andmonitoring its power supply voltage.

Consider, as an example, the monitoring of the status of port A. Tocheck the status of port A, control circuitry 54 may open periodicallyopen switch SWA using control line 62A. This disconnects line 72A andline 58A from the output of converter circuit 122. If an electronicdevice is present on port A, voltage regulator 52A will be unable tosupply all of the current needed by the device. This will cause thevoltage Vbusa that is being monitored on line 60A by control circuitry54 to drop. In this situation, control circuitry 54 can conclude that aload is present on port A. Switch SWA can then be closed to allow normaloperations to continue. If, however, no electronic device is present onport A, the opening of switch SWA will cause the voltage Vbusa on line60A to rise (e.g., to 5.1 volts). When this rise is detected, controlcircuitry 54 can conclude that no load is present on port A. In the sameway, switch SWB may be controlled by control line 62B while voltageVbusb on line 72B and line 58B at the output of voltage regulator 52B isbeing monitored using line 60B.

This type of arrangement may be used by control circuitry 54 todetermine which ports have active loads. If desired, current-sensingresistors such as resistors RA and RB may be used to make load currentmeasurements. With one suitable arrangement, the voltages acrossresistors RA and RB are examined before the scheduled opening ofswitches SWA and SWB. Resistors RA and RB are generally not too large,so as not to impede efficient power delivery to attached devices. As aresult, it can be difficult to use resistors RA and RB to measureextremely low load current values (i.e., load currents of the type thatcan be detected using switches SWA and SWB, voltage regulators 52A and52B, and sensing lines 60A and 60B). Current-sensing resistors RA and RBcan, however, be used to perform current pre-sensing operations. Forexample, control circuitry 54 can examine the voltage across resistorsRA and RB before opening switches SWA and SWB. If a voltage is detectedacross a current-sensing resistor, control circuitry 54 can concludethat the port that is associated with the detected voltage has an activeload. In this situation, there is no need to open the correspondingswitch SWA or SWB and the switch opening operation can be inhibited toavoid possible glitches.

If desired, other circuit arrangements may be used to poll the ports inpower converter 12 to determine whether an electronic device or otherload is connected to that port. The illustrative load monitoringcircuitry of FIG. 2 is merely illustrative.

Once the number of active ports has been determined, control circuitry54 can compute how much power is available for each port. For example,if the total capacity of AC-DC power converter circuit 122 is 10 W andif there is only a single electronic device connected to converter 12,control circuitry 54 may conclude that the entire 10 W capacity ofconverter circuit 122 is available for delivery to the connected device.If, however, there are two electronic devices connected to converter 12,control circuitry 54 may conclude that each port will be able to supply5 W to its associated device. Computing the amount of power availablefor each of the active ports in this way allows the capacity of powerconverter circuit 122 to be intelligently shared between the devicesthat are connected to converter 12. It is therefore not necessary toover-provision the circuitry in converter 12.

Each device 10 that is connected to converter 12 may be informed of theamount of available power from converter 12. In some situations,relatively more power may be available. For example, when a device isthe only device connected to a given power converter, the powerconverter may be able to supply the device with 10 W of power. In othersituations, less power may be available. For example, if there are twodevices connected to the given power converter, the power converter mayonly be able to supply each device with 5 W of power. Devices 10generally contain power management circuitry that can be configured toadjust their power draw levels. When a device is informed that there are10 W of power available, the device may configure its power managementcircuitry so that the device consumes 10 W. When a device is informedthat there are 5 W of power available, the device may configure itspower management circuitry so that the device consumes a reduced powerof 5 W.

By advertising the amount of power that is available for each port(i.e., the per-port available power), converter 12 can reconfiguredevices 10 and can effectively share a limited amount of powerconversion capacity among the devices. Any suitable technique may beused by converter 12 to convey information to devices 10 that informsdevices 10 the per-port power availability. For example, converter 12may include analog communications circuitry, digital communicationscircuitry, circuitry that generates codes based on fixed or time-varyingresistance values, fixed or time-varying current values, or fixed ortime varying voltage values. Coding schemes may present a particularcircuit parameter (resistance, current, voltage, inductance, etc.)across a pair of terminals in a port or may present a series of multiplecircuit parameters (e.g., across a single pair of terminals or acrossmultiple sets of terminals). Combinations of these coding approaches mayalso be used.

With one illustrative configuration, which is sometimes described hereinas an example, converter 12 may include circuitry that presentsvoltage-based codes to devices 10. The voltage-based codes may instructa device to configure its power management circuitry so that the deviceconsumes a particular desired amount of power. The circuitry forproducing the voltage-based codes may be implemented as part of controlcircuitry 54.

Illustrative voltage-coding circuitry of the type that may be used incontrol circuitry 54 is shown in FIG. 3. As shown in FIG. 3,voltage-coding circuitry 100 (which may sometimes be referred to ascommunications circuitry, adjustable voltage divider circuitry, orcoding circuitry), may be formed from parallel voltage dividers VD1 andVD2. Voltage divider VD1 includes series-connected resistors R1 and R2.Voltage divider VD2 may include resistor R3 and an adjustable resistorthat is formed from the parallel combination of resistor R4 (in a firstbranch) and resistor RN and transistor 106 (in a second branch).

Line 102 may be connected to a source of positive voltage (e.g., line64) and line 104 may be connected to ground (e.g., ground terminal 70).In a two-port power converter, there may be one of circuits 100associated with port A and one of circuits 100 associated with port B.In port A, connector terminal Vbus of the first version of circuit 100is connected to terminal P in connector 20A. Connector terminal Vbus ofthe second version of circuit 100 is connected to terminal P inconnector 20B of port B. Similarly, terminals DP and DN in the firstinstance of circuit 100 are associated with DP and DN in connector 20Aand terminals DP and DN in the second instance of circuit 100 areassociated with connector 20B. In the first instance of circuit 100,ground terminal GND is coupled to ground terminal G of connector 20A(line 74A). In the second instance of circuit 100, ground terminal GNDis coupled to ground terminal G of connector 20B (line 74B).

In a typical scenario, line 102 is provided with a positive supplyvoltage at 5 V and line 104 is provided with a ground supply voltage of0 volts. Resistors R1 and R2 may be selected to produce a desired fixedvoltage value V1 on line DP. In voltage divider VD2, a variable voltageV2 may be produced on node N1. Resistor R3 may be coupled between line102 and node N1. A variable resistor may be coupled between node N1 andnode N2.

In the FIG. 3 example, the variable resistor between nodes N1 and N2 hasbeen implemented using the parallel combination of two resistances. Thefirst resistance is a fixed resistance associated with resistor R4. Thesecond resistance varies depending on the state of control switch 106.Control switch 106 may be implemented using a transistor or othersuitable switching circuit. In the example of FIG. 3, switch 106 hasbeen implemented using an n-channel metal-oxide-semiconductor (NMOS)transistor. Control circuitry 54 (FIG. 2) may generate time-varying orstatic control signals CNTL on line 108 at the gate of transistor 106.The value of the control signal CNTL on line 108 determines the state oftransistor 106. If CNTL is high, transistor 106 will be on and drainterminal D will be shorted to source terminal S. If CNTL is low,transistor 106 will be off and will form an open circuit (infiniteresistance) between drain terminal D and source S.

The state of transistor 106 therefore controls the resistance betweennodes N1 and N2. When transistor 106 is off, there is an open circuitbetween drain D and source S, so the resistance between nodes N1 and N2is equal to the resistance of resistor R4. When transistor 106 is on,both of the parallel resistor paths between node N1 and node N2 areactive. In this situation, the resistance between node N1 and N2 isgiven by the parallel combination of R4 and RN (i.e., R4*RN/(R4+RN)).When transistor 106 is off, the voltage V2 has a first (higher) valueassociated with the relative strengths of resistors R3 and R4. Whentransistor 106 is on, the voltage V2 has a second (lower) valueassociated with the relative strengths of resistor R3 and thecombination of resistor R4 in parallel with resistor RN.

With this type of circuit, control circuitry 54 can adjust the values ofV1 and V2. The values of V1 and V2 and/or their relative values can beused as codes. An electronic device that is connected to converter 12can monitor the values of V1 and V2 over the DP and DN lines in a USBcable and can take appropriate action based on the V1 and V2 values. Onecombination of V1 and V2 may, for example, correspond to a situation inwhich the device should be configured to draw 10 W of power (i.e., whenthe per-port available DC power is 10 W) and another combination of V1and V2 may, for example, correspond to a situation in which the deviceshould be configured to draw 5 W of power (i.e., when the per-portavailable DC power is 5 W).

Another circuit that may be used in control circuitry 54 to producedesired values of V1 and V2 on connector terminals DP and DN is shown inFIG. 4. In circuitry 110 of FIG. 4, line 112 may be connected to asource of positive voltage (e.g., line 64 in FIG. 2) and line 114 may beconnected to ground (e.g., ground terminal 70 in FIG. 2). As withcircuit 100 of FIG. 3, there may be a respective one of circuits 110associated with each port in power converter 12. For example, there maybe one of circuits 110 associated with port A and one of circuits 110associated with port B in a two-port configuration.

The values of V1 and V2 that are produced by circuitry 110 may becontrolled by control circuitry 54 by applying appropriate digitalcontrol signals (logic ones and zeros) to the gates G of the controltransistors of circuitry 110. As shown in FIG. 4, circuitry 110 may havea first adjustable voltage divider circuit 110A that produces voltage V1and a second adjustable voltage divider circuit 110B that producesvoltage V2.

Each adjustable voltage divider has a number of branches. Each branchhas an upper segment and a lower segment. The upper segments includep-channel metal-oxide-semiconductor (PMOS) transistors and the lowersegments include n-channel metal-oxide-semiconductor (NMOS) transistors.Each branch also includes a pair of transistors, one of which is in theupper segment of that branch and one of which is in the lower segment ofthat branch. For example, the first branch of circuit 110A (branch B1A)has an upper segment that contains PMOS transistor TP1 and resistor RP1and has a lower segment that contains NMOS transistor TN1 and resistorRN1. The upper segments of the branches of voltage divider 110A may eachhave a different respective resistance (RP1, . . . RPN) and the lowersegments of the branches of voltage divider 110A may likewise each havea different respective resistance (RN1, . . . RNN). By turning on agiven one of the PMOS transistors and a given one of the NMOStransistors in circuit 110A while all other transistors in circuit 110Aare turned off, a desired voltage divider may be formed by circuit 110Aand therefore a desired value of V1 on terminal DP may be produced. Ifdesired, multiple transistors (e.g., multiple NMOS transistors and/ormultiple PMOS transistors) may be turned on at the same time in circuit110A, thereby creating parallel resistance circuits of desiredresistance values. Adjustable voltage divider 110B may be operated inthe same way as adjustable voltage divider 110A to produce a desiredvalue of V2 on terminal DN.

The adjustable voltage divider circuitry of FIGS. 3 and 4 serves as atype of digital-to-analog (D-to-A) converter circuit for producingdesired V1 and V2 values. An illustrative circuit that is based onD-to-A circuits 124 and 126 (e.g., integrated circuit D-to-A circuits)is shown in FIG. 5. In this type of arrangement, control circuitry 123may be implemented using the resources of control circuitry 54. D-to-Aconverters 124 and 126 may also be implemented within circuitry 54. Line118 may receive a positive power supply voltage from line 64 of FIG. 2and ground line 116 may receive a 0 volt ground signal from line 70 ofFIG. 2. Terminals VBUS, DP, DN, and GND may be associated with aconnector in a port in power converter 12. Multiple circuits 116 may beused in converters that include multiple ports.

During load sensing operations, control circuitry 54 may determine theper-port power that is available to the devices that have been connectedto the ports of converter 12. The available per-port power level maythen be communicated to the connected devices. For example, controlcircuitry 123 may provide digital signals to D-to-A converter 124 thatdirect D-to-A converter 124 to produce a desired value of V1 on terminalDP. Control circuitry 123 may also provide digital signals to D-to-Aconverter 126 that direct D-to-A converter 126 to produce a desiredvalue of V2 on terminal DN. Each device 10 may include voltage detectorcircuitry and control logic that can monitor lines DP and DN and thatcan recognize the coded per-port power information being transmitted bycontrol circuitry 123. Each device 10 may then adjusts its power draw toaccommodate the per-port available power from converter 12.

If desired, more complex communications circuits can be used by controlcircuitry 123. For example, D-to-A converters 124 and 126 can be omittedso that control circuitry 123 can be connected directly to terminals DPand DN. An asynchronous or synchronous digital communications link maythen be established over paths DP and DN between converter 12 and eachattached device. This communications link may be unidirectional orbidirectional and may involve the transmission of signals using anysuitable coding scheme.

Illustrative steps involved in using power converter 12 are shown inFIG. 6. Initially, as shown by line 127, a user may decide to connectone or more devices 10 or other loads to respective ports in powerconverter 12.

Power converter 12 may periodically monitor the status of its ports. Forexample, control circuitry 54 may periodically make load currentmeasurements as described in connection with FIG. 2 (step 128). Fromthese measurements, control circuitry 54 can determine which of theports in power converter 12 are connected to loads. If, for example,there are three ports in converter 12 and a user has plugged only asingle device into one of these three ports, control circuitry 54 candetermine that only one device is present. If, as another example, threeseparate electronic devices are plugged into the three ports, controlcircuitry 54 can determine from load measurements that all three portsare occupied.

Following a determination of the number of ports to which electronicdevices have been attached at step 128, power converter 12 can usecontrol circuitry 54 to compute the maximum per-port power available(step 130). For example, if power converter 12 has a converter circuitsuch as circuit 122 with a 10 W capacity and there are three occupiedports, control circuitry 54 will determine that the per-port availablepower level is 10 W divided by three (i.e., 3.33 W). If fewer devicesare connected, the per-port available power level will be larger.

At step 132, control circuitry 54 may advertise the amount of power thatis available on each port. Any suitable communications scheme may beused. For example, control circuitry 54 may use a voltage coding schemeof the type described in connection with FIGS. 3, 4, and 5 to produce aset of voltages V1 and V2 that indicate the value of the per-portavailable power. Schemes based on more complex digital communicationsprotocols (e.g., bidirectional protocols, etc.) may also be used.

Control circuitry 54 may limit the current that is drawn by theconnected devices. For example, control circuitry 54 can monitor theamount of current (and therefore the amount of power) that is deliveredthrough each port by monitoring the voltage drop across current sensingresistors such as resistors RA and RB of FIG. 2. If the power flowing toa given port starts to exceed the maximum allowed per-port limit, thepower flowing to that port can be regulated. For example, controlcircuitry 54 can adjust a control switch that is associated with theport to reduce or interrupt power flow (e.g., by adjusting switch SWA toprevent excessive power from flowing to the device that is connected toport A, by adjusting switch SWB to regulate power flow to port B, etc.).Switches such as switches SWA and SWB may be adjusted using analog ordigital control signals, fixed or time-varying control signals, or anyother suitable control signals to impose desired power limits. Powerregulation can also be performed using circuit 122. Fuses, circuitbreakers, or other power-limiting devices or circuits can also be usedto ensure that power limits are not exceeded.

At step 136, the electronic devices 10 that are attached to powerconverter 12 can receive and decode the encoded per-port available powerinformation that was transmitted from control circuitry 54 during theoperations of step 132. If, for example, there is only a single deviceconnected to converter 12, the device might receive and processinformation that 10 W of power is available from converter 12. Thatdevice may then use its power management circuitry to adjust the amountof power that is being drawn from converter 12 to a matching value(i.e., 10 W). If, however, there were two devices connected to converter12, the devices might each receive and process information indicatingthat 5 W of power is available per port. Each of the two devices maythen use its power management circuitry to adjust its power draw tomatch the available 5 W of power.

As illustrated by line 138, the steps of FIG. 6 involved in using powerconverter 12 may be repeated. For example, the steps of FIG. 6 may berepeated after a user disconnects one or more devices 10 or other loadsfrom their respective ports in power converter 12 (e.g., whenever a userdisconnects one or more of the devices or other loads connected to powerconverter 12). This type of arrangement may help to ensure that devices10 which are still connected to power converter 12 can receive themaximum amount of power available from power converter 12 (e.g., thatpower converter 12 does not reserve power for ports which are no longerconnected to a device or other load). With one suitable arrangement, thesteps of FIG. 6 may be continuously repeated or repeated at certainintervals (e.g., every 5 seconds, every 10 seconds, every 30 seconds,every minute, every five minutes, or at other suitable intervals). Ingeneral, the steps of FIG. 6 may be repeated at any periodic or randominterval.

The foregoing is merely illustrative of the principles of this inventionand various modifications can be made by those skilled in the artwithout departing from the scope and spirit of the invention.

What is claimed is:
 1. An apparatus configured to provide power andpower level data for a plurality of external electronic devices, theapparatus comprising: a plurality of ports; load detection circuitrythat detects when at least one of the plurality of external electronicdevices is connected to the apparatus, wherein the load detectioncircuitry comprises a control switch and a current-limited voltageregulator configured to provide an output voltage larger than a nominalpower supply output voltage; and control circuitry configured to:compute a per-port available power level that varies based on a numberof active loads connected to the plurality of ports, and provide a codeto at least one external electronic device of the plurality of externalelectronic devices, via a data terminal of at least one port of theplurality of ports, wherein the code comprises data corresponding to theper-port available power level available to the at least one externalelectronic device and provides a reference for the at least one externalelectronic device to adjust an amount of power received from the atleast one port.
 2. The apparatus of claim 1, wherein the controlcircuitry comprises voltage divider circuitry that produces at least oneadjustable output voltage for each port of the plurality of ports. 3.The apparatus of claim 1, wherein: each port of the plurality of portsis configured with two data terminals; and the control circuitry adjustsvoltages at the two data terminals to advertise the per-port availablepower level to the at least one external electronic device of theplurality of external electronic devices.
 4. The apparatus of claim 1,wherein the load detection circuitry further comprises a plurality ofcontrol switches, each control switch of the plurality of controlswitches being associated with a respective port of the plurality ofports.
 5. The apparatus of claim 1, wherein the load detection circuitrycomprises a plurality of current-sensing resistors, each current-sensingresistor of the plurality of current-sensing resistors being associatedwith a respective port of the plurality of ports.
 6. The apparatus ofclaim 1, wherein: each port of the plurality of ports is configured withtwo power terminals; and the load detection circuitry comprises aplurality of current-sensing resistors, each current-sensing resistor ofthe plurality of current-sensing resistors being coupled to one of thetwo power terminals.
 7. The apparatus of claim 6, wherein: the loaddetection circuitry further comprises a plurality of current-limitedvoltage regulators; and each current-limited voltage regulator of theplurality of current-limited voltage regulators produces the outputvoltage that is applied at one of the two power terminals.
 8. Theapparatus of claim 7, wherein the load detection circuitry furthercomprises a plurality of switches, each switch of the plurality ofswitches having a terminal that is connected to an output of at leastone of the plurality of current-limited voltage regulators.
 9. Theapparatus of claim 1, wherein the control circuitry comprises adigital-to-analog converter providing at least one analog voltage to atleast one data terminal.
 10. The apparatus of claim 1, furthercomprising an alternating current to direct current converter.
 11. Theapparatus of claim 1, further comprising a plurality of connectors,wherein each connector of the plurality of connectors is configured withtwo power terminals and two data terminals, and is associated with arespective port of the plurality of ports.
 12. A device for managing asupply of power to a plurality of external electronic devices, thedevice comprising: a plurality of ports configured to provide power tothe plurality of external electronic devices; circuitry that detectswhen at least one external electronic device of the plurality ofexternal electronic devices is connected to the device; and controlcircuitry configured to: determine a per-port available power level foreach port of the plurality of ports based on a number of active loadsthat are connected to the plurality of ports, and provide a code to theat least one external electronic device of the plurality of externalelectronic devices, via at least one data terminal of a port of theplurality of ports, wherein the code comprises data corresponding to theper-port available power level for the at least one external electronicdevice and provides a reference for the at least one external electronicdevice to adjust an amount of power received from the port.
 13. Thedevice of claim 12, wherein the control circuitry further comprises adigital-to-analog converter that is coupled to the at least one dataterminal to provide the code to inform the at least one externalelectronic device of the plurality of external electronic devices of theper-port available power level.
 14. The device of claim 12, wherein thecontrol circuitry comprises adjustable voltage divider circuitry. 15.The device of claim 14, wherein the adjustable voltage divider circuitrycomprises a plurality of resistors and at least one transistor having agate that receives a control signal from the control circuitry.
 16. Thedevice of claim 15, wherein the adjustable voltage divider circuitryfurther comprises a plurality of p-channel metal-oxide-semiconductortransistors and a plurality of n-channel metal-oxide-semiconductortransistors connected in a plurality of branches between a positivepower supply line and a ground power supply line.
 17. A method ofoperating an apparatus that includes a plurality of ports that areconfigured to be coupled to at least one external electronic device of aplurality of external electronic devices, the method comprising:determining a number of ports of the plurality of ports that areconnected to an active load; determining a per-port available powerlevel that is available to the at least one external electronic deviceof the plurality of external electronic devices connected to at leastone port of the plurality of ports; and providing a code to the at leastone external electronic device through a data line of the at least oneport, wherein the code comprises data corresponding to the per-portavailable power level for the at least one external electronic device ofthe plurality of external electronic devices and provides a referencefor the at least one external electronic device of the plurality ofexternal electronic devices to adjust an amount of power received fromthe at least one port of the plurality of ports.
 18. The method of claim17, wherein the code includes digital data.
 19. The method of claim 18,wherein the apparatus provides the code to the at least one externalelectronic device of the plurality of external electronic devices usingadjustable voltage divider circuitry.
 20. The method of claim 17,wherein the apparatus provides the code to the at least one externalelectronic device of the plurality of external electronic devices usingbidirectional communication protocols over the data line.